I rode America West a few times when I worked for Intel and we hadn't started the shuttle service. I remember a trip back in 2000 (that bad, yes I remember it) where I had a Sunday evening flight from SEA to PHX, meetings on Monday and then return to SEA Monday (late pm). The flight down was delayed due to a maintenance problem that delayed the northbound arrival into SEA. OK, that happens. Then, on Monday as we were climbing out of PHX my ears were popping very rapidly. The pressurization system on the plane wasn't working. The pilot leveled off at 10,000 MSL, fiddled with the system, couldn't fix it and had to return to PHX. AW said, "no problem, there's another plane at the next gate we can use". Nope. FO did his walk-around and found a squawk that needed maintenance to fix it. In the meantime the next scheduled flight to SEA is getting ready to board and the gate agent (who was awesome, BTW) offered it as an alternative. I took it. It didn't leave on schedule as they couldn't pump water in one of the galleys. 4 airplanes in a row that couldn't make their flights on schedule due to maintenance issues. I wrote a rather strongly worded email to AW and our travel people detailing the problems. I don't recall what, if any, compensation I got from America West, but our travel office was happy to get my email as they were about to enter negotiations with America West for the new travel contract. I guess it helped.
I'm not a fan of AA, and I don't like DL, either. I've ridden DL a number of times since 1976 and every single one of those flights in cattle car have had inadequate leg room. Who do they think they are, Lufthansa?
Yes, I've had bad experiences with United (with just over 1.4 million miles in their seats, what do you expect?), but nothing like my AW experience, or a mess that Alaska caused a number of years ago that resulted in my giving the first day of a two day class in Penang, Malaysia in the clothes I traveled in, without a shave. Interesting trip. Coming home from that one I had my one experience with Evergreen. I'll ride them in their "Evergreen Deluxe Class" anywhere, anytime. Very comfortable business class seats. Especially on coach tickets. I still don't know what happened, but I won't complain. SAS bumped me to Business Class a number of years ago on a leg from Stockholm to Chicago. Business Class on their A-330 back then was very nice and had a feature I haven't seen since - the rest room was large enough and had 2 windows. Windows in the restroom on an airliner?
Travel enough and you'll see all sorts of "stuff".